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Chronology and pyroclastic stratigraphy of the May 18, 1980, eruption of Mount St. Helens, WashingtonThe eruption of Mount St. Helens on May 18, 1980 can be subdivided into six phases: the paroxysmal phase I, the early Plinian phase II, the early ash flow phase III, the climactic phase IV, the late ash flow phase V, and phase VI, the activity of which consisted of a low-energy ash plume. These phases are correlated with stratigraphic subunits of ash-fall tephra and pyroclastic flow deposits. Sustained vertical discharge of phase II produced evolved dacite with high S/Cl ratios. Ash flow activity of phase III is attributed to decreases in gas content, indicated by reduced S/Cl ratios and increased clast density of the less evolved gray pumice. Climactic events are attributed to vent clearing and exhaustion of the evolved dacite.
Document ID
19880024437
Document Type
Reprint (Version printed in journal)
Authors
Criswell, C. William (New Mexico, University Albuquerque, United States)
Date Acquired
August 13, 2013
Publication Date
September 10, 1987
Publication Information
Publication: Journal of Geophysical Research
Volume: 92
ISSN: 0148-0227
Subject Category
GEOPHYSICS
Funding Number(s)
CONTRACT_GRANT: NSF EAR-84-17143
CONTRACT_GRANT: NGR-32-004-062
CONTRACT_GRANT: NSF EAR-85-07028
Distribution Limits
Public
Copyright
Other